Remove code duplication and inconsistencies among different ports by using a single function in the base class for the determination of the effective icon style to use, correctly handling both wxICON_NONE and the absence of any wxICON_XXX styles. Closes #11822. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63725 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775